1. Field of the Invention
The present invention relates to diagnostic devices for generating tomographic images of an exposure subject, and in particular to patient support bodies containing reference elements therein for use in such a device.
2. Description of the Prior Art
The use of reference elements in the generation of computer tomographics is known, the reference elements being comprised of a known composition and having known attenuation values. When scanning an examination subject to produce a computer tomograph, the reference bodies are automatically scanned at the same time and reproduced in the cross-sectional image. A reference measurement utilizing reference bodies positioned close to the patient's body is therefore achieved without burdening the patient. The reference bodies appear in the image in every event, i.e. independent of the particular transversal layer being investigated. The reference bodies enable an automatic self-compensation of the computer tomography system for every measurement, independent of variable system parameters such as beam quality and drift. The reference bodies further enable a quantitative evaluation of transversal layer images and quantitative comparisons of transversal layer images recorded at different computer tomograph installations. The images of the reference bodies in the transversal layer image are not superimposed on the image of the patient.
Patient support units are known in the art wherein the reference bodies are inserted in the housing aperture of the bed which receives the patient, this apparatus having two patient beds disposed at both sides of the housing. The two-bed apparatus, with a gap therebetween, is outdated and modern support systems now comprise only one bed which extends through the housing aperture of the apparatus. Arrangement of the reference bodies in this manner is therefore no longer possible. In modern patient support systems, it is known to rigidly attach the reference bodies in the inside of the bed. This results in a relatively expensive structure for the bed and moreover it is not possible to individually select the reference bodies which are to be used for a particular scan, that is, it is not possible to undertake replacement of reference bodies or to remove them as needed.
Another reference body arrangement is described in "Precise Measurement Of Vertebral Mineral Content Using Computed Tomography", Cann et al., Journal Of Computer Assisted Tomography, 1980, at pages 493-500. This unit is a plexiglass member which is matched in form to that of the bed surface, and which has a plurality of bores filled with different solutions. This plexiglass member is placed on the bed surface and the patient is seated thereon. This system has the disadvantages of the size of the unit, the difficulty of comfortably placing the patient thereon, and of the relatively high beam attenuation which is achieved by the unit. Moreover, this arrangement is well-suited only for examinations of the trunk region.
Lastly, it is also known to secure reference bodies to a belt which is placed around the patient. This technique, however, is also relatively involved.